1. Field of the Invention
This invention relates to a radiation image read-out apparatus for exposing stimulable phosphor sheets carrying a radiation image stored thereon respectively to stimulating rays which cause them to emit light in proportion to the stored radiation energy, and detecting and converting the emitted light into electric signals. This invention particularly relates to a radiation image read-out apparatus in which a plurality of the stimulable phosphor sheets are subjected to image read-out in an arbitrary order.
1. Description of the Prior Art
When certain kinds of phosphors are exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays or ultraviolet rays, they store a part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted by the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed in U.S. Pat. Nos. 4,258,264, 4,276,473, 4,315,318 and 4,387,428 and Japanese Unexamined Patent Publication No. 56(1981)-11395, it has been proposed to use a stimulable phosphor in a radiation image recording and reproducing system. Specifically, a sheet provided with a layer of the stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet) is first exposed to a radiation passing through an object such as the human body to have a radiation image of the object stored thereon, and is then scanned with stimulating rays which cause it to emit light in proportion to the stored radiation energy. The light emitted by the stimulable phosphor sheet upon stimulation thereof is photoelectrically detected and converted to an electric image signal, which is processed as desired to reproduce a visible image having an improved quality, particularly a high diagnostic efficiency and accuracy. The finally obtained visible image may be reproduced in the form of a hard copy or may be displayed on a cathode ray tube (CRT). In this radiation image recording and reproducing system, the stimulable phosphor sheet is used to temporarily store the radiation image in order to reproduce the final visible image therefrom on a final recording medium. For economical reasons, therefore, it is desirable that the stimulable phosphor sheet be used repeatedly.
In order to reuse stimulable phosphor sheets as described above, the radiation energy remaining on the stimulable phosphor sheet after it is scanned with stimulating rays to read out the radiation image stored thereon should be released by exposure to light or heat as described in, for example, Japanese Unexamined Patent Publication No. 56(1981)-12599 or U.S. Pat. No. 4,400,619. The stimulable phosphor sheet should then be used again for radiation image recording. Accordingly, the applicant proposed in, for example, Japanese Patent Application No. 59(1984)-220740 a radiation image read-out apparatus which conducts image read-out from a stimulable phosphor sheet and erasing of residual radiation energy as mentioned above.
In the case where image read-out is conducted by use of the radiation image read-out apparatus provided with an image read-out section and an erasing section as mentioned above, for example, when it is found that radiation image recording conducted on a stimulable phosphor sheet was incorrect after the stimulable phosphor sheet is fed to the radiation image read-out apparatus, it is desired to send the stimulable phosphor sheet directly to the erasing section without conducting image read-out to erase the stored radiation energy, thereby more quickly making the sheet reusable for image recording. Also, when in the radiation image read-out apparatus there are stimulable phosphor sheets carrying a radiation image stored thereon on which image read-out has not been carried out, it is often desired to conduct urgent image read-out on a different stimulable phosphor sheet preferentially to the aforesaid stimulable phosphor sheets and quickly observe the radiation image stored on the stimulable phosphor sheet.
However, in the conventional radiation image read-out apparatus provided with the image read-out section and the erasing section, the image read-out section and the erasing section are connected by, for example, an endless belt device, and the stimulable phosphor sheet must always be passed through the image read-out section when it is sent to the erasing section. Therefore, a long time is required for the sending operation, and the waiting time until the next image read-out becomes long.
In order to make the aforesaid preferential image read-out possible, it has been proposed in, for example, Japanese Unexamined Patent Publication No. 58(1983)-72044, to dispose a stack zone and a by-pass feed system for changing the order of the sheet feed to the image read-out section between a stimulable phosphor sheet receiving section and the image read-out section. In this case, since the stimulable phosphor sheet is passed through a complicated sheet feed system composed of endless belts, nip rollers or the like, the sheet is easily scratched or dust readily clings to the sheet because of electrostatic attraction.